The recovery of chlorinated poly(vinyl chloride), ("CPVC") in its solid state is generally not a problem because it is produced by the chlorination of solid poly(vinyl chloride) ("PVC") which remains solid both during and after it is chlorinated. Thus, whether the PVC is chlorinated with gaseous chlorine ("Cl.sub.2 ") as a suspension in an inert liquid medium (which liquid does not react with PVC), whether the liquid medium is aqueous or nonaqueous, or whether chlorination is effected either thermally or in the presence of ultraviolet light, the solid CPVC formed is recovered by the relatively simple expedient of separating the solid CPVC from the liquid phase in which the solid CPVC is suspended. Most commercially used CPVC is produced by the chlorination of an aqueous suspension of PVC such as is described in U.S. Pat. No. 2,996,489, and recovery of the solid CPVC is by centrifuging and drying. On the other hand, if PVC is chlorinated in a fluid bed of solids by reaction with gaseous chlorine, the separation problem is avoided altogether.
In a recently discovered process described in copending application Ser. No. 228,538 filed Jan. 28, 1981, now U.S. Pat. No. 4,350,798, the disclosure of which is incorporated by reference thereto as if fully set forth herein, there is described a process for the chlorination of solid PVC in a liquid Cl.sub.2 medium which simultaneously serves a three-fold function. Liquid Cl.sub.2 provides the medium in which the PVC is suspended; it is the essential reactant which effects chlorination of the PVC, and it is a solvent for the CPVC after it is formed, resulting in a syrup-like solution. The problem arises when one desires to recover the CPVC in solid form. The CPVC must first be precipitated from the solution in solid form, and the solid must then be separated from the liquid.
Chlorination of PVC in solution ("solution chlorination") is well-known. The CPVC is known to be recovered from its solution by evaporation of the solvent leaving a solid hard mass of CPVC which is difficult to pulverize even at relatively low temperatures. To obtain a finely divided solid, the mass of CPVC obtained is preferably dissolved in a solvent such as hot tetrahydrofuran (THF) and recovered from such a solution by concentrating the THF. Still another method of recovering solid finely divided CPVC from its solution in liquid Cl.sub.2 is to pour the solution into methanol. This produces a mass of irregularly shaped large solids rather than a powder which is preferred if not essential in the marketplace. Neither of the foregoing methods for recovering solid CPVC from its solution in liquid Cl.sub.2 is economically desirable. The method of recovery of this invention provides a simple, convenient and economical method of obtaining solid CPVC in a desirable finely divided form.